Abstract: The present invention relates to a Raman amplifier and the like which has a structure capable of easily improving the transient response characteristic without depending on the added/dropped signal channels. In the Raman amplifier, a pumping light source supplies forward pumping light of wavelength &lgr;p0 to a Raman-amplifying optical fiber. A pumping light source supplies N-channel backward pumping light of wavelengths &lgr;p1-&lgr;pN to the Raman-amplifying optical fiber. The wavelength &lgr;p0 of the forward pumping light is less than or equal to the shortest wavelength of the channel wavelengths &lgr;p1-&lgr;pN of the backward pumping light. In particular, the power of the backward pumping light and the power of the forward pumping light are arranged such that the effective length Leff of the Raman-amplifying optical fiber for the channel wavelengths &lgr;p1-&lgr;pN of the backward pumping light becomes longer than the actual length L.

Abstract: Raman amplification pumping light output from a pumping light source unit is supplied to a Raman amplification optical fiber through an optical circulator. The remaining Raman amplification pumping light is detected by a light-receiving element through an optical circulator and bandpass filter. Signal light that has reached a Raman amplifier propagates through the Raman amplification optical fiber while being Raman-amplified. A control section controls the power or spectral shape of Raman amplification pumping light output from each of N pumping light sources included in the pumping light source unit on the basis of the power of the remaining Raman amplification pumping light, which is detected by the light-receiving element. Hence, a Raman amplifier capable of easily controlling gain spectrum flattening in the signal light wavelength band can be obtained.

Abstract: The present invention relates to a fabrication method of an optical fiber product and others capable of effectively restraining increase of loss near the wavelength of 1.38 &mgr;m induced by OH-radical absorption. The fabrication method of the optical fiber product involves the steps of preparing two optical fibers with mutually different mode field diameters, and heating a region near a splice end face of at least one optical fiber with the smaller mode field diameter by a heating source not using a fuel containing pure hydrogen as a constitutive element, before or after a fusion splice is made between these optical fibers. This reduces the OH-radical absorption in the heated region, so as to decrease the increase of transmission loss at the wavelength of 1.38 &mgr;m to 0.1 dB or less.

Abstract: The present invention relates to an optical fiber component for Raman amplification having a construction for effectively suppressing deterioration of the transmission characteristic caused by amplification of scattered light components. The optical fiber component for Raman amplification has an optical fiber for Raman amplification and is inserted at a position where the effective deterioration amount of the optical SN ratio produced by DRBS-XT (Double Rayleigh Back Scattering-Crosstalk) is 1 dB or less at the signal output terminal of the optical fiber for Raman amplification.

Abstract: The present invention relates to a dispersion compensating fiber module excellent in pumping efficiency. The dispersion compensating fiber module includes a dispersion compensating optical fiber for compensating for a chromatic dispersion of an optical transmission line through which signal light propagates, and an optical fiber that can function as a Raman amplification optical fiber. The optical fiber that can function as a Raman amplification optical fiber, in particular, has the characteristics including an FOM Raman of 8 (1/dB/W) or more with respect to signal light having a wavelength of 1,650 nm when pumping light having a wavelength of 1,550 nm is supplied, and a chromatic dispersion with an absolute value of 10 ps/nm/km to 50 ps/nm/km at the wavelength of 1,650 nm.

Abstract: The present invention provides a Raman amplification pumping module and others with a structure for effectively suppressing degradation of quality of signal light even with a breakdown in either one of a plurality of light sources. The Raman amplification pumping module is provided with light sources for emitting respective lightwaves with center wavelengths different from each other, and each of the center wavelengths of the lightwaves from these light sources is adjusted so that a difference between two center wavelengths selected therefrom is less than 6 nm.

Abstract: The present invention relates to a Raman amplifier where flexibility in device design considering both of Raman amplification and dispersion compensation is high. In the Raman amplifier, the Raman amplification optical fiber included in the optical amplification section and the dispersion compensating optical fiber included in the dispersion compensation section are arranged while being optically connected to each other. Since the optical amplification section and the dispersion compensation section are provided as independent optical devices, one device can be designed without being restricted to the design conditions of the other device.

Abstract: The present invention relates to an optical communication system having a flat gain spectrum and an excellent pumping efficiency in a signal wavelength band, and comprising a structure which is realizable/operable at a low cost. This optical communication system comprises an optical transmission line including a plurality of Raman amplification optical fibers, and pumping light suppliers for supplying pumping light to the Raman amplification optical fibers. In particular, two Raman amplification optical fibers selected from the plurality of Raman amplification optical fibers included in the optical transmission line differ from each other in at least one of the wavelength at which the gain of Raman amplification becomes the highest, and the number of channels at which the gain of Raman amplification is maximum.

Abstract: Disclosed are a gain module and an optical communication system which have gain in a broad wavelength range and are of low cost. The gain module 10 has two optical fibers 111 and 112 which differ from each other with respect to the composition of their respective optical waveguide region and which are connected in series. Because they differ from each other with respect to the quantity of their respective Stokes shift, they have gain in a different wavelength, respectively. The signal lights are introduced into the input end 10a, amplified with the gain module 10 in a wide wavelength range where an optical fiber has a Raman amplification gain, and are emitted from the output end 10b.

Abstract: Raman amplification pumping light output from a pumping light source unit is supplied to a Raman amplification optical fiber through an optical circulator. The remaining Raman amplification pumping light is detected by a light-receiving element through an optical circulator and bandpass filter. Signal light that has reached a Raman amplifier propagates through the Raman amplification optical fiber while being Raman-amplified. A control section controls the power or spectral shape of Raman amplification pumping light output from each of N pumping light sources included in the pumping light source unit on the basis of the power of the remaining Raman amplification pumping light, which is detected by the light-receiving element. Hence, a Raman amplifier capable of easily controlling gain spectrum flattening in the signal light wavelength band can be obtained.

Abstract: An optical transmission path in a Raman gain module (1) for transmitting signal light input from an input terminal (1a) and Raman-amplifying the signal light by pumping light supplied from pumping light source units (21, 22) is formed by connecting in series two Raman amplification optical fibers (11, 12) having different wavelength dispersion values. According to this arrangement, wavelength dispersion in the amplifier module (1) can be controlled using, e.g., the combination of the wavelength dispersion values of the Raman amplification optical fibers (11, 12). Hence, accumulation of dispersion into signal light and signal light transmission in an almost zero dispersion state are prevented, and degradation in signal light transmission quality due to the nonlinear optical effect is suppressed.